Preheat oven to 400 degrees.
In a small bowl combine chili powder, cumin, salt, garlic powder and onion powder.
Place thinly sliced chicken, bell peppers and onions in a large bowl and sprinkle with the spices tossing until everything is well coated.
Spread the chicken and vegetables on a parchment paper lined or greased, sheet pan.
Bake for 15 minutes or until chicken is cooked through. Warm tortillas while waiting.
When fajitas are ready, fill tortillas with chicken and veggies!